Note: Descriptions are shown in the official language in which they were submitted.
CA 02483509 2004-10-25
WO 03/092027 PCT/US03/12449
FUSE CUTOUT WITH IMPROVED DROPOUT PERFORMANCE
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to an improved fuse cutout and, more
particularly, to an improved fuse cutout that has increased dropout
characteristics
and operating performance. The improved fuse cutout of the present invention
is of
the type shown in S&C Electric Co. Descriptive Bulletin 351-30, dated December
7,
1998, entitled "S&C Type XS Fuse Cutouts" and in U.S. Patent Nos.: 2,553,098;
2,745,923 and 4,414,527. This type of fuse cutout may be used with a fuse link
of
the type sold by S&C Electric Co. as the Positrol~ Fuse Link and as generally
shown
in U.S. Pat. Nos. 4,317,099.
Discussion of the Prior Art
Fuse cutouts and fuse links utilized therein are well known. A typical fuse
cutout includes a hollow insulative fuse tube having conductive ferrules
mounted to
the opposite ends thereof. One ferrule (often called the "exhaust" ferrule) is
located
at an exhaust end of the fuse tube and usually includes a trunnion which
interfits
with a trunnion pocket or hinge of a first contact assembly carried by one end
of an
insulator. The other ferrule is normally held and latched by a second contact
assembly carried by the other end of the insulator so that the fuse tube is
normally
parallel to, but spaced from, the insulator. The insulator is mountable to the
cross-
arm of a utility pole or a similar structure. The fuse link is located within
the fuse
tube with its ends respectively electrically continuous with the ferrules. One
point of
an electrical circuit is connected to the first contact assembly, while
another point of
the circuit is connected to the second contact assembly. Often, the insulator
and the
fuse tube are oriented generally perpendicular to the ground so that the
exhaust
ferrule and the first contact assembly are located below the other ferrule and
the
second contact assembly. The fuse tube may include a high burst strength outer
portion--for example, a fiber-glass-epoxy composite having an arc-
extinguishing
material within the inner portions thereof. Normal currents flowing through
the
electrical circuit flow without affecting the fuse link. Should a fault
current or other
over-current, to which the fuse link is designed to respond, occur in the
circuit, the
fuse link operates as described in more detail hereinafter.
-1 -
CA 02483509 2004-10-25
WO 03/092027 PCT/US03/12449
Operation of the fuse link permits the upper ferrule to disengage itself from
the upper contact assembly, whereupon the fuse tube rotates downwardly due to
coaction of the trunnion and the hinge. If the fuse link operates properly,
current in
the circuit is interrupted and the rotation of the fuse tube gives a visual
indication
that the cutout has operated to protect the circuit, e.g. dropout operation to
a so-
called dropout position. Typical fuse links include a first terminal and a
second
terminal, between which there is normally connected a fusible element made of
pure
silver, silver-tin, or the like. Also connected between the terminals may be a
strain
wire, for a purpose described below. The second terminal is electrically
continuous
with, and is usually mechanically connected to, a button assembly, which is
engagable by a portion of the upper ferrule on the fuse tube. The first
terminal is
connected to a flexible, stranded length of cable. Surrounding at least a
portion of
the second terminal, the fusible element, the strain wire (if used), the first
terminal,
and some portion of the flexible stranded cable is a sheath. The sheath is
typically
made of a so-called ablative arc-extinguishing material which, when exposed to
the
heat of a high-voltage arc, ablate to rapidly evolve large quantities of
deionizing
turbulent and cooling gases. Typically, the sheath is much shorter than the
fuse tube
and terminates short of the exhaust end of the fuse tube.
The free end of the stranded cable exits the fuse tube from the exhaust end
thereof and has tension or pulling force maintained thereon by a spring-loaded
flipper on the trunnion. The tension or pulling force exerted on the cable by
the
flipper attempts to pull the cable and the first terminal out of the sheath
and out of
the fuse tube. The force of the flipper is normally restrained by the strain
wire,
typical fusible elements not having sufficient mechanical strength to resist
this
tension or pulling force. In the operation of typical cutouts, a fault current
or other
over-current results, first, in the melting or vaporization of the fusible
element,
followed by the melting or vaporization of the strain wire. Following such
melting or
vaporization, a high-voltage arc is established between the first and second
terminals within the sheath and the flipper is now free to pull the cable and
the first
terminal out of the sheath and, ultimately, out of the fuse tube. As the arc
forms, the
arc-extinguishing materials of the sheath begin to ablate and high quantities
of de-
ionizing, turbulent and cooling gases are evolved. The movement of the first
terminal under the action of the flipper, and the subsequent rapid movement
thereof
due to the evolved gases acting thereon as on a piston, results in elongation
of the
arc. The presence of the de-ionizing, turbulent and cooling gas, plus arc
elongation,
-2-
CA 02483509 2004-10-25
WO 03/092027 PCT/US03/12449
may, depending on the level of the fault current or other over-current,
ultimately
result in extinction of the arc and interruption of the current at a
subsequent current
zero. The loss of the tension on the stranded cable permits the trunnion to
experience some initial movement relative to the exhaust ferrule which permits
the
upper ferrule to disengage itself from the upper contact assembly. This
initiates a
downward rotation of the fuse tube and its upper ferrule to a so-called
"dropout" or
"dropdown" position.
As noted above, arc elongation within the sheath and the action of the
evolved gases may extinguish the arc. At very high fault current or over-
current
levels, however, arc elongation and the sheath may not, by themselves, be
sufficient
to achieve this end. Simply stated, at very high fault current levels, either
the sheath
may burst (because of the very high pressure of the evolved gas) or
insufficient gas
may be evolved therefrom to quench the high current level arc. For these
reasons,
the fuse tube is made of, or is lined with, ablative arc-extinguishing
material. In the
event the sheath bursts, the arc-extinguishing material of the fuse tube
interacts with
the arc, with gas evolved as a result thereof achieving arc extinction. If the
sheath
does not burst, the arc-extinguishing material of the fuse tube between the
end of
the sheath and the exhaust end of the fuse tube is nevertheless available for
evolving gas, in addition to that evolved from the sheath. The joint action of
the two
quantities of evolved gas, together with arc elongation, extinguish the arc.
When a fuse tube is properly positioned between the upper and lower contact
assemblies of the mounting, the contacts of the fuse tube are firmly engaged
within
the contact assemblies of the mounting. When the fuse link operates, gases
evolved
within the fuse tube thrust it against the upper contact assembly of the
mounting.
Ideally, the contact cap should not disengage the concavity until the fusible
elements
of the fuse link completely melts to release the tension in the cable and
until the
initial thrust of the fuse tube subsides. Release of this tension and
subsiding of fuse
tube thrust permits a limited amount of relative movement between the exhaust
ferrule and the trunnion about a toggle joint therebetween. This limited
movement
permits the contact cap to move out of the concavity and the fuse tube to
begin
movement toward the dropout position due to rotation of the trunnion in the
hinge
pocket. If the fuse tube moves too far transversely during its thrusting, the
contact
cap may disengage the concavity too early. Third, transverse movement of the
fuse
tube can apply a bending movement thereon. This bending movement can fracture
-3-
CA 02483509 2004-10-25
WO 03/092027 PCT/US03/12449
the fuse tube near the exhaust ferrule. Corrosion that builds up on various
parts and
dimensional changes of the fuse tube or fuse link sheath, e.g. due to
environmental
factors, can exacerbate the proper dropout action.
Thus, it is important for achieving proper operation as explained above that
dropout operation be readily achieved in spite of any deleterious operating
environments or conditions.
SUMMARY OF THE INVENTION
Accordingly, it is a principal object of the present invention to provide a
cutout
with improved dropout performance.
This and other objects of the present invention are achieved by an improved
fuse cutout of the type having a fuse tube assembly that moves to a dropout
position
upon operation in response to a fault current or other overcurrent. These
types of
fuse cutouts include the pivotal mounting of the fuse tube assembly with
respect to a
support hinge with the fuse tube assembly being released for pivotal movement
to
the dropout position when the fuse cutout has operated. The fuse tube assembly
includes a collapsible toggle joint that collapses upon operation of the fuse
cutout.
The improved fuse cutout includes additional dropout assistance that is
provided via
a resilient member operating between the components of the collapsible toggle
joint
to apply a force to assist the collapse of the toggle joint.
DESCRIPTION OF THE DRAWING
FIG. 1 is a perspective view of an improved fuse cutout according
to the present invention;
FIG. 2 is an elevational view of a fuse tube assembly of the cutout of FIG. 1;
FIG. 3 is an enlarged, partial view of the fuse tube assembly of FIG. 2 in an
operative position; and
FIG. 4 is an enlarged elevational view of a dropout assist member of the
cutout of FIGS. 1-3.
DETAILED DESCRIPTION
Referring first to FIG. 1, there is shown an improved cutout 12 according to
the present invention that includes an insulator 14 and a mounting member 16
extending therefrom. The mounting member 16 permits mounting of the insulator
14
and the fuse cutout 12 to an upright or a crossarm of a utility pole or the
like (not
-4-
CA 02483509 2004-10-25
WO 03/092027 PCT/US03/12449
shown). Affixed to the upper end of the insulator 14 is an upper contact
assembly
generally designated 18. Further, affixed to the lower end of the insulator 14
is a
lower contact assembly 20. The cutout 12 also includes a fuse tube assembly 22
(also shown in FIG. 2) that in the normal, circuit-connected or unoperated
condition
of the cutout 12 may be maintained in the generally vertical position shown in
FIG. 1,
e.g. cutouts are typically mounted at a slight angle to the vertical.
Considering now more specific features of the fuse tube assembly 22, the
fuse tube assembly includes an insulative fuse tube 24 of a well-known type,
which
may comprise an epoxy-fiber-glass composite outer shell lined with an arc-
extinguishing material. Mounted or affixed to the upper end of the fuse tube
24 is an
upper ferrule assembly 26, while at the opposite lower or exhaust end of the
fuse
tube 24 is a lower or exhaust ferrule assembly 28. In the position of the fuse
tube
assembly 22 depicted in FIG. 1, the lower ferrule assembly 28 is held by the
lower
contact assembly 20, while the upper ferrule assembly 26 is held, and latched
against movement, by the upper contact assembly 18.
The upper contact assembly 18 includes a support bar 30 and a recoil arm
and contact hood 32 which runs generally parallel to a portion of the support
bar 30.
Near the top of the insulator 14, the bar 30 and the arm 32 are mounted by a
fastener or the like at 36 to a portion of a connector assembly 40 that is
affixed to
the top of the insulator 14. The connector assembly 40 facilitates the
connection to
the upper contact assembly 18 to a cable or conductor of a high-voltage
circuit.
The upper contact assembly 18 also includes a spring contact arm 42 and a
backup spring 44 that is positioned between the spring contact arm 42 and the
recoil
arm and contact hood 32, e.g. the backup spring 44 is positioned at one end
over a
convexity 45 extending from the top of the contact arm 42 and at the other end
over
a convexity (not shown) extending downwardly from the recoil arm and contact
hood
32. The backup spring 44 provides high contact pressure between the contact
arm
42 and the top of the fuse tube assembly 24 as will be explained in more
detail
hereinafter. As is typical in the power industry, the support bar 30 at a
downwardly
bent portion 35 includes attachment hooks 48 for cooperation with a portable
loadbreak tool.
The upper ferrule assembly 26 of the fuse tube assembly 24 includes a
ferrule 50 affixed to the upper end of the fuse tube 24. The ferrule 50
typically
includes a threaded portion (not shown) onto which is threaded a contact cap
52.
The contact cap 52 is configured so as to fit into and be held when the fuse
tube
-5-
CA 02483509 2004-10-25
WO 03/092027 PCT/US03/12449
assembly 22 is in the position shown in FIG. 1, e.g., by an indentation or
concavity
(not shown) formed in the spring contact 42 opposite the convexity 45. The
ferrule
50 typically also includes a pull ring 54. The pull ring 54 may be engaged by
a hook
stick or the like to move the upper ferrule assembly 26 away from the upper
contact
assembly 18 while the lower ferrule assembly 28 rotates in the lower contact
assembly 20, as described hereinafter.
In view of the nature of high voltage circuits, this opening movement of the
fuse tube assembly 22 must be effected while the circuit connected to the
cutout 10
is de-energized or else an arc will form between the upper ferrule assembly 26
and
the upper contact assembly 18. The fuse tube assembly 22 may also be opened by
initially attaching between the attachment hooks 48 and the pull ring 54 a
portable
loadbreak tool. Such a portable loadbreak tool permits the fuse tube assembly
22 to
be opened with the circuit energized, momentarily having transferred thereto
the flow
of current in the circuit 10 and interrupting such current internally thereof.
The lower contact assembly 20 includes a support member 56 attached to a
mount 58 by a fastener or the like at 60. The support member 56 carries a
connector
62, such as a parallel groove connector, to facilitate connection of the lower
contact
assembly 20 to another cable or conductor of the high-voltage circuit in which
the
fuse cutout 12 is to be used. The support member 56 provides a hinge function
via
trunnion pockets 64. The trunnion pockets are designed to cooperate with and
hold
outwardly extending portions 66 of a trunnion 68 (also shown in FIG. 3)
carried by
the fuse tube 24. Specifically, a lower ferrule 72 affixed to the fuse tube 24
pivotally
mounts the trunnion 68 at a toggle joint 70. Thus, the trunnion 68 functions
as a
toggle member and defines a double pivot mounting for the fuse tube 24, the
first
pivot being defined at the toggle joint 70 and the second pivot being defined
by the
extending portions 66 of the trunnion 68 within the trunnion pockets 64 of the
hinge
support member 56.
As hereinafter described, the trunnion 68 and the ferrule 72 are normally
rigidly held in the relative position depicted in FIG. 1. In this normal
relative position
of the trunnion 68 and the ferrule 72, the contact cap 52 is engaged by the
spring
contact 42 to maintain the fuse tube assembly 22 in the position depicted in
FIG. 1.
Also, as described in more detail below, when a fuse link (not shown) within
the fuse
tube 24 operates, the trunnion 68 and the ferrule 72 are no longer rigidly
held, and
the ferrule 72 may rotate downwardly relative to the trunnion 68 about the
toggle
joint 70. This movement of the ferrule 72 permits the contact cap 52 to
disengage
-6-
CA 02483509 2004-10-25
WO 03/092027 PCT/US03/12449
the spring contact 42, following which the entire fuse tube assembly 22
rotates about
the lower contact assembly 20 via rotation of the extending portions 66 in the
trunnion pockets 64. Considering additional structural features, rotatably
mounted to
the trunnion 68 is a flipper 74. A spring 75 mounted between the trunnion 68
and
the flipper 74 biases the flipper 74 away from the lower or exhaust end of the
fuse
tube 24. The trunnion 68 includes shoulders 76 or other similar features. The
support member 56 also includes features, such as shoulders 78, normally
spaced
from the shoulders 76 when the extending portions 66 of the trunnion 68 are
seated
in their respective trunnion pockets 64. The normal spacing between the
shoulders
76 and 78 is sufficient to permit appropriate movement of the fuse tube 24
with
respect to the lower contact assembly 20 during operation as explained
hereinafter.
In use, a fuse link is first installed into the fuse tube assembly 22. Suffice
it
here to say that the contact cap 52 is removed and the fuse link is inserted
into the
interior of the fuse tube 24 from the upper end thereof. A portion of the fuse
link
abuts a shoulder (not shown) at the top of the ferrule 50, following which the
contact
cap 52 is threaded back onto the ferrule 50. Reference may be made to S&C
Electric Co. Instruction Sheet 351-500 and the aforementioned patents for
additional
information and details. A flexible stranded cable 80 forming a part of the
fuse link
exits an exhaust opening at 81 in the lower or exhaust end of the fuse tube
24. The
flipper 74 is manually rotated against the action of the spring 75 to position
it
adjacent the exhaust opening at 81 following which the cable 80 is laid into a
channel at 82 in the flipper 74. Following this, the cable 80 is wrapped
around a
flanged bolt 84 (shown in FIGS. 2-4) that is threaded into the trunnion 68 via
a
threaded portion 85. Following tightening of the flanged bolt 84 to hold the
cable 80,
the flipper 74 is maintained against the bias of the spring 75 in the position
shown in
FIG. 1, whereat there is a constant tension force applied to the cable 80 and
the
remainder of the fuse link within the fuse tube 24. It is this connection of
the cable
80 to the trunnion 68 by the flanged bolt 84 and the action of the spring 75
on the
flipper 74 that normally holds the trunnion casting 68 and the ferrule 72 in
the
position depicted in FIG. 1 relative to the toggle joint 70.
Following operation of a fuse link within the fuse tube 24, the flipper 74 is
able
to move the cable 80 downwardly within the fuse tube 24. The release of the
tension
force applied to the cable 80 by the flipper 74 permits relative movement of
the
ferrule 72 and the trunnion 68 about the toggle joint 70 to permit separation
of the
contact cap 52 from the spring contact 42. The relative movement of the
ferrule 72
-7-
CA 02483509 2004-10-25
WO 03/092027 PCT/US03/12449
and the trunnion 68 occurs after tension in the cable 80 is released and after
an
initial upward thrust of the fuse tube 24 subsides. As more fully explained in
the
aforementioned patents, when a fusible element (not shown) of the fuse link
within
the fuse tube 24 melts, there follows the rapid evolution of arc-extinguishing
gas
within the fuse tube 24. This evolved gas exits the exhaust opening at 81of
the fuse
tube 24 at a very rapid rate, thrusting the fuse tube 24 upwardly.
When the fuse link operates, the tension on the cable 80 is released at the
same time the fuse tube 24 thrusts up. While the relative movement of the
trunnion
68 with respect to the ferrule 72 and about the toggle joint 70 does not
immediately
occur simultaneously with the rapid gas exhaust, it is able to occur shortly
thereafter
in response to the release of tension in the cable 80. This relative movement
permits the contact cap 52 to disengage from the contact arm 42 and the fuse
tube
assembly 22 to rotate to a "dropout" position via rotation of the extensions
66 of the
trunnion 68 in the trunnion pockets 64. All of the above is "timed" so that
rotation of
the fuse tube assembly 22 is initiated as or after the fuse link has
interrupted current
in the circuit.
There is a tendency for frictional resistance caused by corrosion,
contamination or sleet such that the trunnion 68 may not be able to pivot
about the
hinge support member 56. If that should occur, the fuse tube 24 would remain
in
place and not dropout, thus not providing the desirable and necessary air gap
to
prevent leakage over the fuse tube 24. To this end, an anvil surface 86 is
provided
on the lower surface of the trunnion 68 that is engaged by the upper edges 88
of the
spaced sidewalls 90 of the flipper 74. Thus, the impact of the flipper 74 as
well as
the action of the spring 75 act to assist in pivoting the trunnion 68 about
the toggle
joint 70. In some circumstances it may be desirable and/or necessary to
further
improve the dropout performance, especially where 1. the fuse link or fuse
tube
components might experience dimensional changes due to environmental factors
and/or 2. where the cutout mounting and fuse tube assembly are from different
manufacturers which may not be ideally suited to work with each other, i.e.
the
interfacing, cooperating components are not identical to those for which they
were
designed.
In accordance with important aspects of the present invention, additional
dropout assistance is provided via a spring 92 carried about the shaft of the
bolt 84,
e.g. the shaft of the bolt 84 having a narrowed portion 94 beyond the wider,
. 35 threaded shaft portion 96. Ina specific embodiment, the narrowed portion
94
_g_
CA 02483509 2004-10-25
WO 03/092027 PCT/US03/12449
includes a threaded portion 98 for affixing the spring 92 to the bolt 84. The
spring 92
is compressed when the bolt 84 is threaded into the trunnion 68 and tightened
to
hold the cable 80. The spring 92 is compressed against an extending tab 100 of
the
ferrule 72 of the lower ferrule assembly 28. Accordingly, when the fuse
operates
and the cable 80 is released, the spring 92 acts to directly rotate the
trunnion 68
about the toggle joint 70 to assist in the dropout action of the fuse tube
assembly 22.
It should be noted that this assist action is more positive than that of the
pivoting of
the trunnion 68 due to its being released and also over a wider range and time
than
that of the release of the flipper 74.
Accordingly, the bolt 84 with the spring 92 as an overall assembly 104
performs a dropout assistance function and also functions to retain or clamp
the
cable 80 to maintain the fuse tube assembly within the upper and lower contact
assemblies 18 and 20. It should also be noted that since every fuse cutout of
the
type 12 utilizes a bolt such as 84 to clamp the cable 80, the dropout
assistance
assembly 104 is capable of easy retrofit in the field merely by substituting
the
dropout assistance assembly 104 for the conventional bolt for clamping the
cable
80. Further, the desired additional dropout assistance is variable in specific
embodiments via the selection of the resilient characteristics of the spring
92. It will
also be clear to those skilled in the art that the leading surface of the
spring 92
and/or the extending tab 100 of the ferrule 72 of the lower ferrule assembly
28
should be prepared and/or finished so as to provide unfettered rotation of the
spring
92 when tightening the bolt 84 during installation of the fuse link as well as
reliable
disengagement thereof during operation of the fuse cutout 12.
While there have been illustrated and described various embodiments of the
present invention, it will be apparent that various changes and modifications
will
occur to those skilled in the art. Accordingly, it is intended in the appended
claims to
cover all such changes and modifications that fall within the true spirit and
scope of
the present invention.
_g_
